US5444621A - Suspension control system for controlling suspension of automotive vehicle based on wheel speed data - Google Patents

Suspension control system for controlling suspension of automotive vehicle based on wheel speed data Download PDF

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Publication number
US5444621A
US5444621A US07/896,930 US89693092A US5444621A US 5444621 A US5444621 A US 5444621A US 89693092 A US89693092 A US 89693092A US 5444621 A US5444621 A US 5444621A
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United States
Prior art keywords
vehicle
wheel speed
control system
signal
wheel
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US07/896,930
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English (en)
Inventor
Eiju Matsunaga
Akira Fukushima
Noriyuki Nakashima
Toshiyuki Murai
Shinya Takemoto
Mikio Tanabe
Hisashi Kinoshita
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Denso Corp
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NipponDenso Co Ltd
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Assigned to NIPPONDENSO CO., LTD. reassignment NIPPONDENSO CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: MURAI, TOSHIYUKI, TANABE, MIKIO, KINOSHITA, HISASHI, NAKASHIMA, NORIYUKI, TAKEMOTO, SHINYA, FUKUSHIMA, AKIRA, MATSUNAGA, EIJU
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
    • B60G17/015—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements
    • B60G17/016—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by their responsiveness, when the vehicle is travelling, to specific motion, a specific condition, or driver input
    • B60G17/0165—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by their responsiveness, when the vehicle is travelling, to specific motion, a specific condition, or driver input to an external condition, e.g. rough road surface, side wind
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2202/00—Indexing codes relating to the type of spring, damper or actuator
    • B60G2202/40—Type of actuator
    • B60G2202/42—Electric actuator
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2204/00—Indexing codes related to suspensions per se or to auxiliary parts
    • B60G2204/80—Interactive suspensions; arrangement affecting more than one suspension unit
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2400/00—Indexing codes relating to detected, measured or calculated conditions or factors
    • B60G2400/20—Speed
    • B60G2400/204—Vehicle speed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2401/00—Indexing codes relating to the type of sensors based on the principle of their operation
    • B60G2401/10—Piezoelectric elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2500/00—Indexing codes relating to the regulated action or device
    • B60G2500/10—Damping action or damper
    • B60G2500/104—Damping action or damper continuous
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60G—VEHICLE SUSPENSION ARRANGEMENTS
    • B60G2600/00—Indexing codes relating to particular elements, systems or processes used on suspension systems or suspension control systems
    • B60G2600/60—Signal noise suppression; Electronic filtering means

Definitions

  • the present invention relates a suspension control system for controlling a suspension of an automotive vehicle.
  • the known suspension control systems need various sensors for detecting the road surface condition. For example, a stroke sensor for detecting a relative displacement of the suspension, a sprung acceleration sensor for detecting the behavior of a sprung structure of the suspension, and many other sensors must be mounted on the vehicle. These sensors make the suspension control system complicated in construction as a whole, are likely to case problems when they are mounted on teh vehicle, and increase the production cost of the suspension control system.
  • a specific object of the present invention is to provide a suspension control system which includes a small number of sensors and hence is simple in construction and can be manufactured less costly, and is able to improve the riding comfort and maneuverability of the vehicle.
  • the present invention is based on the experimental findings that the wheel speed of an automotive vehicle is susceptible to change according to the road surface condition and the degree of change of the wheel speed is closely related to the roughness of a road surface on which the vehicle is running. This means that the road surface condition can be estimated from the wheel speed. It is also true that a sprung structure and an unsprung structure of a suspension will resonate in accordance with the road surface condition.
  • the present inventors have devised an improved suspension control system in which a road surface condition is detected on the basis of a wheel speed and, in accordance with the detected road surface condition, the stiffness of the suspension is altered so that the riding comfort and maneuverability of the vehicle are improved.
  • a suspension control system for controlling a suspension of an automotive vehicle having a wheel, comprising: wheel speed detection means for detecting a rotational speed of the wheel of the vehicle and generating a wheel speed signal corresponding to the detected rotational speed of the wheel, the wheel speed signal containig a first resonance frequency component having a sprung resonance frequency of the suspension, and a second resonance frequency component having an sprung resonance frequency of the suspension; extraction means, coupled to the wheel speed detection means, for extracting at least one of the first and second resonance frequency components from the wheel speed signal; and altering means, coupled to the extraction means, for altering the stiffness of the suspension on the basis of said at least one resonance frequency component extracted by the extraction means.
  • a wheel speed is detected and, based on the detected wheel speed, a signal containing at least one of a sprung resonant frequency component and an unsprung frequency component is outputted. From the signal thus outputted is extracted a signal containing a resonance frequency component based on which the stiffness of a suspension is altered.
  • FIG. 1 is a block diagram showing the principle of a suspension control system according to a first preferred embodiment of the present invention
  • FIG. 2 is a partial cross-sectional view of a shock absorber of an automotive vehicle in which the suspension control system is installed;
  • FIG. 3 is an enlarged cross-sectional view of a main part of the shock absorber
  • FIG. 4 is a flowchart illustrating the operation of the suspension control system according to the first embodiment of the present invention
  • FIG. 5 is a diagram illustrating how to control the suspension according to the first embodiment of the present invention.
  • FIG. 6 is a graph used for setting reference values K b and K c ;
  • FIG. 7 is a graph used for setting a reference value K d ;
  • FIG. 8 is a graph used for setting a reference value K 0 ;
  • FIG. 9 is a graph used for setting a reference value K 1 ;
  • FIG. 10 is a graph used for setting a reference value K 2 ;
  • FIG. 11 is a graph used for setting a reference value K 3 ;
  • FIG. 12 is a graph showing the relationship between a vehicle speed and force exerted on an axle due to a roughness on a road surface
  • FIG. 13 is a flowchart illustrating a main portion of a control operation according to a second preferred embodiment of the present invention.
  • FIG. 14 is a flowchart illustrating a main portion of a control operation according to a third preferred embodiment of the present invention.
  • FIG. 15 is a flowchart illustrating a main portion of a control operation according to a fourth preferred embodiment of the present invention.
  • FIG. 16 is a flowchart illustrating a main portion of a control operation according to a fifth preferred embodiment of the present invention.
  • FIG. 17 is a flowchart illustrating the operation of a seventh preferred embodiment of the present invention.
  • FIG. 18 is a diagram illustrating characteristics explanatory of the operation of the seventh embodiment.
  • FIG. 19 is a graph illustrating the relationship between a sprung vibration estimation signal V US and a long-term vibration judgement level X;
  • FIG. 20 is a graph illustrating the relationship between a road surface condition signal dV SP and a road surface judgement level x;
  • FIG. 21 is a map used for setting a damping force based on the long-term vibration judgment level x and the road surface judgement level x;
  • FIG. 22 is a flowchart illustrating the operation of an eighth preferred embodiment of the present invention.
  • FIG. 23 is a flowchart illustrating the operation of a tenth preferred embodiment of the present invention.
  • FIG. 24 is a map showing the relationship between the signals dV a , dV B and ⁇ V B and a correction coefficient K H ;
  • FIG. 25 is a flowchart illustrating the operation of an eleventh preferred embodiment of the present invention.
  • FIGS. 26A through 26C are maps illustrating the relationship between a vehicle speed and a delay period
  • FIG. 27 is a diagram showing cutoff frequencies of filters
  • FIG. 28 is a diagram showing the degree of filters
  • FIG. 29 is a flowchart illustrating the operation of a fifteenth preferred embodiment of the present invention.
  • FIG. 30 is a map showing the relationship between the road surface condition signal dV SP and the correction coefficient K H ;
  • FIG. 31 is another map showing the relationship between the road surface condition signal dV SP and the correction coefficient K H ;
  • FIG. 32A through 32C are maps showing the relationship between the vehicle speed and the correction coefficient
  • FIG. 33 is a map showing the relationship between the road surface condition signal dV SP and the delay period
  • FIG. 34 is a flowchart illustrating the operation of the eighteenth preferred embodiment of the present invention.
  • FIG. 35 is a map showing the relationship between an estimated vehicle speed V B and a flatting judgment basic level
  • FIG. 36 is a map showing the relationship between the road surface condition signal dV SP and correction coefficients K M , K H ;
  • FIG. 37 is a diagram illustrating how threshold levels are corrected
  • FIG. 38 is a flowchart illustrating the operation of a nineteenth preferred embodiment of the present invention.
  • FIG. 39 is a diagram showing the relationship between the estimated vehicle speed V B and an attitude change judgment level Y;
  • FIG. 40 is a map showing the relationship between the estimated vehicle speed V B and a steering angle ⁇ ;
  • FIG. 41 is a diagram showing the relationship between a stop lamp switch judgment STP, a longitudinal direction acceleration dV B , and the attitude change judgment level Y;
  • FIG. 42 is a diagram showing the relationship between a throttle opening judgment THR, the longitudinal direction acceleration dV B and the attitude change judgment level Y;
  • FIG. 43 is a map used for setting a damping force from the attitude change judgment level Y and the road surface judgment level x;
  • FIG. 44 is a flowchart illustrating the operation of a twentieth preferred embodiment of the present invention.
  • FIG. 45 is a map showing the relationship between the estimated vehicle speed V B and the steering angle ⁇ ;
  • FIG. 46 is a map showing the relationship between the estimated vehicle speed V B and dive judgment basic levels 1 DC , 1 DB ;
  • FIG. 47 is a map showing the relationship between the estimated vehicle speed V B and squat judgment basic levels 1 SC , 1 SD ;
  • FIG. 48 is a map showing the relationship between the road surface condition signal dV SP and roll judgment correction coefficients K RB , K RC ;
  • FIG. 49 is a map showing the relationship between the road surface condition signal dV SP and dive judgment correction coefficients K DC , K DB ;
  • FIG. 50 is a map showing the relationship between the road surface condition signal dV SP and squat judgment correction coefficients K SC , K SB ;
  • FIG. 51 is a flowchart illustrating the operation of a twenty-first preferred embodiment of the present invention.
  • FIG. 52 is a diagram explanatory of the operation of the twenty-first embodiment of the present invention.
  • FIG. 53 is a flowchart illustrating the operation of a twenty-second preferred embodiment of the present invention.
  • FIG. 54 is a diagram explanatory of the operation of the twenty-second embodiment of the present invention.
  • FIG. 55 is a map showing the relationship between the estimated vehicle speed V B and a judgment level K a and a return level K b ;
  • FIG. 56 is a flowchart illustrating the operation of a twenty-third preferred embodiment of the present invention.
  • FIG. 57 is a diagram explanatory of the operation of the twenty-third embodiment of the present invention.
  • FIG. 58 is a flowchart illustrating the operation of a twenty-fourth preferred embodiment of the present invention.
  • FIG. 59 is a map showing the relationship between the vehicle speed and a judgment level K C and a return level K D ;
  • FIG. 60 is a diagram illustrating how the twenty-fourth embodiment operates
  • FIG. 61 is a flowchart illustrating the operation of a twenty-fifth preferred embodiment of the present invention.
  • FIG. 62 is a map showing the relationship between the vehicle speed and the steering angle ⁇ ;
  • FIG. 63 is a diagram illustrating the operation of the twenty-fifth embodiment of the present invention.
  • FIG. 64 is a block diagram showing the general construction of a twenty-sixth preferred embodiment of the present invention.
  • FIG. 65 is a diagram illustrating the operation of the twenty-sixth embodiment of the present invention.
  • FIG. 66 is a map used for judging the road surface condition from a sprung resonance frequency component and an unsprung resonance frequency component;
  • FIG. 67 is a flowchart illustrating the operation of the twenty-sixth preferred embodiment of the present invention.
  • FIG. 68 is a block diagram showing the general construction of a twenty-seventh preferred embodiment of the present invention.
  • FIG. 69 is a flowchart illustrating the operation of the twenty-seventh embodiment of the present invention.
  • FIG. 1 is a block diagram showing the general construction of a first embodiment of the invention, which embodiment is so constructed as to switch the damping force of each shock absorber for altering the stiffness of a suspension.
  • numerals 11, 12, 13 and 14 are wheel speed sensors each producing a speed signal having a frequency proportional to the number of rotation of a corresponding one of a right front wheel (FR), a left front wheel (FL), a right rear wheel (RR) and a left rear wheel (RL).
  • Numeral 16 is a microcomputer coupled with the wheel speed sensors 11-14 and outputs control signals to driver circuits 17-20.
  • the microcomputer 16 is constructed as an arithmetic and logic unit including a central processing unit (CPU) 16A, a read-only memory (ROM) 16B, a random access memory (RAM) 16C, and an input/output unit (I/O) 16D that are well-known per se.
  • CPU central processing unit
  • ROM read-only memory
  • RAM random access memory
  • I/O input/output unit
  • the shock absorbers 21, 22, 23, 24 are of the type which is capable of changing its damping force between two states.
  • Each of the shock absorbers 21-24 is provided between a vehicle body (not shown) and a suspension lower arm (not shown) for a corresponding one of the right front wheel (FR), left front wheel (FL), right rear wheel (RR) and left rear wheel (RL), together with a coil spring (not shown).
  • the shock absorbers 21-24 each include a built-in piezoelectric load sensor and a piezoelectric actuator pair, as will be described later on.
  • the piezoelectric road sensors in the shock absorbers 21-24 detect force exerted on the shock absorbers 21-24, respectively.
  • the piezoelectric actuators in the shock absorbers 21-24 switch the setting of damping force generation patterns relative to the strokes of the respective shock absorbers 21-24.
  • shock absorbers 21-24 Since all the shock absorbers 21-24 are identical in construction, only the shock absorber 21 provided for the right front wheel (FR) is described for the sake of convenience. It will be noted that when there is no difference among the four shock absorbers 21-24, suffixes such as FR, FL, RR and RL are omitted.
  • the shock absorber 21 is fixed to a suspension lower arm (not shown) through a wheel-shaft-side member 51a at a lower end of a cylinder 51.
  • the shock absorber 21 is fixed, together with a coil spring 8, to a vehicle body 7 through a bearing 7a and a rubber cushion element 7b at an upper end of a rod 53 which penetrates into the cylinder 53.
  • an internal cylinder 15 Inside the cylinder 51, there are provided an internal cylinder 15, a connecting member 56 and a cylindrical member 57 which are coupled to the lower end of the rod 53, as well as a main piston 58 which is slidable along an inner surface of the cylinder 51.
  • a piezoelectric load sensor 25 and a piezoelectric actuator 27 are accomodated in the internal cylinder 15 connected to the rod 53 of the shock absorber 21.
  • the main piston 58 is provided outside of the cylindrical member 57 and engages therewith.
  • a seal member 59 is provided between a circumferential outer surface of the main piston 58 and the inner surface of the internal cylinder 15.
  • An internal space of the cylinder 51 is separated into a first fluid chamber 61 and a second fluid chamber 63 by the main piston 58.
  • a backup member 28 is threaded to the front end of the cylindrical member 57.
  • the backup member 28 presses a spacer 29 and a leaf valve 30 against the cylindrical member 57 together with the main piston 58. In this state, the spacer 29 and the leaf spring 30 are fixed.
  • a leaf valve 31 and a collar 32 are provided between the backup member 28 and the main piston 58.
  • the lead valve 31 and the collar 32 are pressed against the backup member 28 and fixed thereto in this state.
  • a main valve 34 and a spring 35 are interposed between the leaf valve 31 and the backup member 28.
  • the main valve 34 and the spring 35 urge the leaf valve 31 toward the main piston 58.
  • the leaf valves 30 and 31 close an expansion-side path 58a and a contraction-side path 58b provided in the main piston 58 on a single side of both the expansion-side path 58a and the contraction-side path 58b.
  • the paths 58a and 58b are opened on respective single sides thereof in accordance with a movement of the main piston 58 indicated by the arrow A or B.
  • a working fluid filled in the first and second fluid chamber 61 and 63 passes through one of the paths 58a and 58b so that it moves between the first fluid chamber 61 and the second fluid chamber 63.
  • both the piezoelectric load sensor 25 and the piezoelectric actuator 27 provided inside the internal cylinder 15 are electrostriction element laminated members in which thin plates formed of piezoelectric ceramics are laminated through electrodes. In other words, one electrode is elevationally sandwiched between two adjacent thin plates.
  • Each of the piezoelectric thin plates in the piezoelectric load sensor 25 is polarized due to a force exerted on the shock absorber 21, that is a damping force.
  • An electrical output signal from each of the piezoelectric thin plates in the piezoelectric load sensor 25 is supplied to an impedance circuit, which generates a voltage signal.
  • an impedance circuit which generates a voltage signal.
  • the piezoelectric actuator 27 has laminated electrostriction elements, each of which expands or contracts with a high response characteristic when a high voltage is applied thereto.
  • the piezoelectric actuator 27 directly drives a piston 36.
  • a plunger 37 and a spool 41 having a substantially H-shaped cross section are moved in the same direction through the movement of the working fluid in an oil-tight chamber 33.
  • the spool 41 is moved from the position shown in FIG. 3 (original position) in the direction of the arrow B, a sub fluid path 56c connected to the first fluid chamber 61 and a sub fluid path 39b in a bush 39 connected to the second fluid chamber 63 become connected to each other.
  • the sub fluid path 39b further becomes connected to a fluid path 57a in the cylindrical member 57 through an oil hole 45a formed in a plate valve 45.
  • the movement of the spool 41 in the direction of the arrow B causes an increase in the amount of working fluid which is transferred between the first fluid chamber 61 and the second fluid chamber 63.
  • the damping characteristic of the shock absorber 21 is altered from a large damping force (“HARD”) state to a small damping force (“SOFT”) state.
  • HARD large damping force
  • SOFT small damping force
  • the degree of movement of the leaf valve 31 provided on the lower surface of the main piston 58 is controlled by the spring 35 in comparison with the leaf valve 30.
  • An oil hole 45b having a diameter greater than that of the oil hole 45a is formed in the plate valve 45 at a position farther from the center of the plate valve 45 than the oil hole 45a.
  • An oil refilling path 38 is provided together with a check valve 38a between the oil-tight chamber 33 and the first fluid chamber 61 so that the amount of working fluid in the oil tight chamber 33 is fixed.
  • FIG. 4 is a flowchart illustrating a shock-absorber damping force control procedure (routine) executed by the microcomputer 16 based on the outputs of the wheel speed sensors 11-14.
  • This control procedure (routine) is performed independently with respect to each of the shock absorbers 21-24 of the respective wheels. Since the control procedure (routine) is common to all the wheels, the control procedure (routine) will be described below without distinction of individual wheels.
  • step A110 when an ignition key switch to the microcomputer 16 is closed, the microcomputer 16 achieves initialization at step A110. Then, step A120 reads or inputs a wheel speed V W . Subsequently, step A130 computes an estimated vehicle speed V B of the vehicle based on the input wheel speed V W . More concretely, the maximum value among four wheel speeds is used for the estimated vehicle speed V B , in the same manner as done in an anti-skid control operation. Alternatively, taking into account of a condition where the vehicle is making a turn, the average value of left and right wheel speeds may be set to the estimated vehicle speed V B .
  • Step A140 computes acceleration dV B in a longitudinal direction (i.e., moving direction) of the vehicle body based on the estimated vehicle speed V B computed at step A130.
  • the acceleration dV B is used as a judgment signal for discerning a sign of the occurrence of anti-squat and anti-dive motions, as described later.
  • the acceleration dV B may be computed either by obtaining a rate of change of the estimated vehicle speed V B computed at step A130, or alternatively from a rate of change of the wheel speed V W inputted at step A120, as disclosed in Japanese Patent Publication No. 1-47324.
  • step A150 estimates a steering angle ⁇ from the difference between the left and right wheel speeds.
  • the steering angle ⁇ is calculated in accordance with the following equation. ##EQU1## where N is the steering gear ratio, L is the wheel base, W is the tread, K is the stability factor, V WFR is the wheel speed of right front wheel, and V WFL is the wheel speed of left front wheel.
  • the steering angle ⁇ is estimated and computed by a speed difference between two front wheels, however, it is possible to estimate the steering angle ⁇ through a calculation based on a speed difference between two rear wheels.
  • step A160 After the wheel speed V W , estimated vehicle speed V B , acceleration dV B and steering angle ⁇ are obtained at steps A120-A150, respectively, the control procedure advances to step A160 onward.
  • Step A160 compares the estimated vehicle speed V B with a reference value K a for judging whether or not a high speed response operation is necessary. If V B ⁇ K a , it is judged that the vehicle is running at a high speed. Then, the control procedure advances to step A250 at which the damping force of the shock absorber is set to the hard state so that it is possible to improve the stability of the vehicle running at high speeds. On the other hand, if V B ⁇ K a , then the control procedure proceeds to step A170.
  • Step A170 compares the acceleration d VB with a reference value K b for judging whether or not an anti-squat control operation is necessary. If dV B >K b , it is judged that the vehicle is in a suddenly accelerated condition. Then, the control procedure advances to step A250. Thus, the damping force of the shock absorber is set to the hard state so that the vehicle body is prevented from squatting or tilting backward. On the other hand, if dV B ⁇ K b , the control procedure proceeds to step A180.
  • Step A180 compares the acceleration d VB with a reference value -K c for judging whether or not an anti-dive control operation is necessary. If dV B ⁇ -K c , it is judged that the vehicle is in a suddenly decelerated condition. Then, the control procedure advances to step A250 at which the damping force of the shock absorber is set to the hard state so that the vehicle body is prevented from diving or tilting forward. On the other hand, if dV B ⁇ -K c , the control procedure proceeds to step A190.
  • Step A190 compares the steering angle ⁇ with a reference value K d for judging whether or not an anti-roll control operation is necessary. If d ⁇ >K d , it is judged that the vehicle is rolling. Then, the control procedure advances to step A250 at which the damping force of the shock absorber is set to the hard state, so that the rolling of the vehicle body is prevented. On the other hand, if ⁇ K d , the control procedure proceeds to step A200.
  • the reference value -K c used at step A170 and the reference value K d used at step A180 may be fixed values, or alternatively they may be determined by using maps which are prepared in conjunction with the estimated vehicle speed V B , as shown in FIGS. 6 and 7.
  • Steps A200-A240 estimate the roughness of a road surface from a change of the wheel speed, in order to control the damping force of the shock absorber.
  • step A200 computes a speed difference V Wa by subtracting the estimated vehicle speed V B from the wheel speed V W in accordance with the following equation (2).
  • This procedure is achieved to remove an offset value which is produced by the vehicle speed when a variation of the wheel speed caused by a roughness on a road surface is to be extracted.
  • Steps A210 and A220 are executed in succession for controlling the sprung vibrations.
  • This sprung vibration control operation is performed to suppress or dampen a "long-term vibration" which will occur due to the presence of a roughness on a road surface such as on an undulated or wavy road surface.
  • the long-term vibration of the automative vehicle has a long term approximately equal to one second and causes a car sickness.
  • the frequency of the long-term vibration is substantially equal to a sprung resonance frequency (about 1.0-2.0 Hz).
  • the speed difference V Wa signal is subjected to a band-pass filtering process using a band-pass filter which passes components having frequencies around a sprung resonance frequency in the range of 1 to 2 Hz.
  • step A220 the filtered speed difference V Wb is compared with two reference values K 0 and K 1 .
  • K 0 ⁇ V Wb or K 1 >V Wb it is judged that the vehicle is continuously running on a wavy road and a complex road such as shown in FIG. 5(a).
  • step A250 the damping force of the shock absorber is set to the hard state as shown in FIG. 5(a) so that the long-term vibration of the vehicle is suppressed and, hence, the riding comfort of the vehicle is improved.
  • K 1 ⁇ V Wb ⁇ K 0 the control procedure proceeds to step A230.
  • the speed difference V Wa signal is subjected to a filtering process using a band-pass filter which components having frequencies around an unsprung resonance frequency in the range of 10 to 15 Hz.
  • the speed difference signal is amplified and thus a filtered speed difference V Wc is computed.
  • the thus computed filtered speed difference V Wc is as shown in FIG. 5(d).
  • the control procedure proceeds to step A240 at which the filtered speed difference V Wc is compared with two reference values K 2 and K 3 . In this instance, when K 2 ⁇ V Wc or K 3 >V Wc , it is judged that the vehicle is continuously running on a busy road and a complex road such as shown in FIG.
  • step A250 the damping force of the shock absorber is set to the hard state as shown in FIG. 5(e) so that the road holding characteristic of the tires is improved and thus the maneuvering stability of the vehicle increases.
  • step A260 the damping force of the shock absorber is set to the soft state.
  • T a predetermined period of time
  • this hard-state setting continues at least for the predetermined time period T.
  • the damping force of the shock absorber is continuously set on the hard state unless the timer counter T is reset to 0 (zero).
  • the reference values K 0 , K 1 , K 2 and K 3 may be fixed values. Alternatively, in view of the fact that a force exerted on a wheel axle due to irregularities on a road surface depends on the vehicle speed (see, FIG. 12), these reference values may be determined on the basis of the estimated vehicle speed V B with the use of maps such as shown in FIGS. 8 through 11.
  • step A250 or step A260 After the setting of the damping force of the shock absorber has completed at step A250 or step A260, the control procedure returns to step A120.
  • a speed difference signal V Wa obtained by subtracting an estimated vehicle speed V B from a wheel speed V W is subjected to first and second filtering processes to extract a first signal containing sprung resonance frequency components and a second signal containing unsprung resonance frequency component. These signals are amplified and first and second filtered speed difference signals V Wb and V Wc are obtained. Each of the filtered speed difference signals V Wb and V Wc is compared with two reference values so that the damping force of the shock absorber is set in accordance with to the road surface condition. For instance, when the vehicle is running continuously on a wavy road and a complex road shown in FIG.
  • a sprung structure of the vehicle will resonate greatly with the result that the filtered speed difference V Wb obtained by the band-pass filtering process for the sprung resonance frequency components has a great absolute value, as shown in FIG. 5(c).
  • the filtered speed difference V Wb exceeds the reference values, as shown in FIG. 5(c) with the result the damping force of the shock absorber is set to the hard state for a predetermined period of time, as shown in FIG. 5(e).
  • the vehicle is running continuously on a busy road and a complex road such as shown in FIG.
  • an unsprung structure of the vehicle resonates greatly and, hence, the filtered speed difference V Wc obtained after the band-pass filtering process for the unsprung resonance frequency components has a great absolute value, as shown in FIG. 5(d).
  • the filtered speed difference V Wc exceeds the reference values, as shown in FIG. 5(d) so that the damping force of the shock absorber is set to the hard state for the predetermined period of time, as shown in FIG. 5(e).
  • the damping force of the shock absorber is switched only by means of information based on the wheel speed detected by the wheel speed sensor, so that the riding comfort and running stagbility of the vehicle are improved.
  • the speed difference signal V Wa obtained by subtracted the estimated vehicle speed V B from the wheel speed V W is subjected to two filtering processes using a band-pass filter for sprung resonance frequency components and a band-pass filter for unsprung resonance frequency components. After the band-pass filtering process, the speed difference signal is amplified and thus a filtered speed difference signal is computed.
  • the second embodiment is characterized in that in place of steps A200-A240 shown in FIG. 4, the wheel speed V W is directly subjected to a band-pass filtering process effected with respect to each of the sprung vibration and the unsprung vibration, as shown in FIG. 13. A description given below is limited to these features shown in FIG. 13 which are different from those shown in FIG. 4.
  • step B120 the wheel speed V W signal is subjected to a band-pass filtering process using a band-pass filter passing sprung resonance frequency components having frequencies in the range of 0.3 to 3 Hz.
  • the wheel speed signal is amplified and thus a filtered wheel speed V Wb2 is computed.
  • the control procedure proceeds to step B220 at which the filtered wheel speed V Wb2 is compared with two reference values K 02 and K 12 . In this instance, when K 02 ⁇ V Wb2 or K 12 >V Wb2 , it is judged that the vehicle is running on a wavy road and a complex road, and based on this judgment, the control procedure advances to step A250.
  • step A250 the damping force of the shock absorber is set to the hard state so that a long-term vibration of the vehicle is suppressed. Thus, the riding comfort of the vehicle is improved.
  • the control procedure proceeds to step B230.
  • step B230 the wheel speed V W signal is subjected to a band-pass filtering process using a band-pass filter which passes unsprung resonance frequency components having frequencies in the range of 10 to 15 Hz.
  • the wheel speed signal is amplified and thus a filtered wheel speed V Wc2 is computed.
  • the control procedure proceeds to step B240 at which the filtered wheel speed V Wc2 is compared with two reference values K 22 and K 32 . In this instance, if K 22 ⁇ V Wc2 or K 32 >V Wc2 , it is judged that the vehicle is running on a busy road and a complex road and, hence, an unsprung structure is vibrating greatly.
  • step A250 the damping force of the shock absorber is set to the hard state so that it is possible to improve the road holding characteristic of the tires and increase the maneuvering stability of the vehicle.
  • step A260 the damping force of the shock absorber is set to the soft state.
  • the reference values K 02 , K 12 , K 22 and K 32 may be fixed values or may be determined based on the estimated vehicle speed V B .
  • step A210 is followed by step C211.
  • Step C211 judges whether or not the estimated vehicle speed V B is greater than or equal to a predetermined value K V3 (for example, 20 km/h).
  • K V3 for example, 20 km/h.
  • the control procedure goes on to step A220.
  • the control procedure advances to step A260 at which the damping force of the shock absorber is set to the soft state.
  • the damping force of the shock absorber is set to the soft state.
  • suspension control system according to a fourth preferred embodiment of the present invention.
  • the suspension control system according to this embodiment partly differs in operation from that of the first embodiment described above with reference to the flowchart shown in FIG. 4. More specifically, the procedures executed at steps A200-A240 shown in FIG. 4 are replaced by the procedures shown in FIG. 15.
  • step D205 computes an angular acceleration dV W of the wheel on the basis of the wheel speed V W calculated at step A120. In this instance, computation is carried out by obtaining a rate of change of the wheel speed V W .
  • a sprung vibration control process is executed in the same manner as done in the first embodiment described above.
  • the angular acceleration dV W signal is subjected to a band-pass filtering process using a band-pass filter which passes sprung resonance frequency components having frequencies in the range of 1 to 2 Hz. With this filtering process, a filtered angular acceleration dV Wb is computed.
  • the control procedure advances to step D225 at which the filtered angular acceleration dV Wb is compared with two reference values K 0 ' and K 1 '.
  • step A250 the damping force of the shock absorber is set to the hard state so that the occurrence of a long-term vibration is suppressed.
  • the control procedure advances to step D235.
  • step D235 the angular acceleration dV W signal is subjected to a band-pass filtering process using a bandpass filter which passes unsprung resonance frequency components having frequencies in the range of 10-15 hz.
  • a filtered angular acceleration dV Wc is computed.
  • the control procedure advances to step D245 at which the filtered angular acceleration dV Wc is compared with two reference values K 2 ' and K 3 '. In this instance, if K 2 ' ⁇ dV Wc or K 3 '>dV Wc , it is judged that unsprung vibrations of the vehicle are great and, based on this judgment, the control procedure goes on to step A250.
  • step A250 the damping force of the shock absorber is set to the hard state with the result that the road holding characteristic of the tires is improved and the steering stability of the vehicle is increased.
  • step D245 the result at step D245 is K 3 ' ⁇ dV Wc ⁇ K 2 '
  • the control procedure advances to step A260 at which the damping force of the shock absorber is set to the soft state.
  • the reference values K 0 ', K 1 ', K 2 ' and K 3 ' may be fixed values. Alternatively, they may be determined based on the estimated vehicle speed V B in the same manner as done in the first embodiment because a force exerted on the wheel axle due to the presence of a roughness on a road surface depends on the vehicle speed.
  • each of the filtered angular accelerations dV Wb and dV Wc are compared with two reference values for setting the damping force of the shock absorber in accordance with the road surface condition. Accordingly, likewise the first embodiment, the fourth embodiment is also able to switch the damping force of the shock absorber to improve the riding comfort and driving stability by using only information based on the wheel speed detected by the wheel sensor.
  • step D245 may be replaced by a bad road judgment process which is disclosed in Japanese Patent Laid-open Publication No. 60-596.
  • the control procedure advances to step A250 and, hence, the damping force of the shock absorber is set to the hard state.
  • the control procedure goes on to step A260 at which the damping force of the shock absorber is set to the soft state.
  • a suspension control system will be given below in conjunction with the fourth embodiment.
  • a band-pass filtering process using an unsprung band-pass filter passing unsprung resonance components having frequencies in the range of 10 to 15 Hz is effected against the angular acceleration dV W signal to compute a filtered angular acceleration dV Wc , as described above with reference to step D235 shown in FIG. 15.
  • the angular acceleration dV W signal is subjected to a band-pass filtering process using a band-pass filter which passes vibration components having frequencies in the range of 1 to 20 Hz.
  • a filtered angular acceleration dV Wc5 computed through the filtering process is compared with two reference values for setting the damping force of the shock absorber.
  • the effect of the vehicle speed during accelerated and decelerated conditions is controlled, while at the same time, the stiffness of the suspension is changed according to the filtered angular acceleration dV Wc5 containing those frequency components (1-20 Hz) tending to deteriorate the riding comfort which range between the sprung resonance frequency and the unsprung resonance frequency.
  • the frequency band of the band-pass filter may be in the range of from a level slightly higher than the sprung resonance frequency to the unsprung resonance frequency (i.e., 3-20 Hz).
  • the sixth embodiment is a modification of the fourth embodiment shown in FIG. 15.
  • the angular acceleration dV W signal is filtered with an unsprung band-pass filter having a frequency band ranging from 10 to 15 Hz, so as to calculate the filtered angular acceleration dV Wc .
  • This step D235 is replaced with step F215 in the sixth embodiment which is executed after step D205.
  • step F215 a low-pass filtering process with a frequency of 20 Hz is effected against the angular acceleration dV W signal to remove noise and calculate a filtered angular acceleration dV Wc6 .
  • the filtered angular acceleration dV Wc6 is then compared with two reference values K 0 ' and K 1 ' at step F225 for setting the damping force of the shock absorber.
  • step F235 is executed to discern an accelerated or decelerated condition of the vehicle through a judgement as to whether or not any of the following conditions (a)-(c) is satisfied.
  • the estimated vehicle speed V B is smaller than a predetermined speed V 20 (for example, 20 km/h);
  • a predetermined time period T E6 for example, 0.3 sec.
  • a predetermined time period T EGF (for example, 0.3 sec.) has not elasped since the shift of an engine angular acceleration from a first state where the absolute value of engine angular acceleration
  • step A260 for setting the damping force of the shock absorber to the soft state.
  • step A250 the damping force of the shock absorber is set to the hard state.
  • a suspension control system according to a seventh preferred embodiment of the present invention will be described below with reference to a flowchart shown in FIG. 17.
  • a control operation shown in FIG. 17 is characterized in that sprung information about the long-term vibration is combined with unsprung information about the road surface condition (i.e. the roughness of a road surface) so as to soften a feeling of jolting or bumpy riding (hereinafter referred to as "bumpy feeding") caused by a roughness on the road surface and also prevent the generation of a long-term vibration, at the same time.
  • road surface condition i.e. the roughness of a road surface
  • step G100 a microcomputer incorporated in the suspension control system performs initialization at step G100.
  • step G110 a wheel speed V W is read or inputted in the microcomputer.
  • step G120 computes an estimated vehicle speed V B of the vehicle from the input wheel speed V W . More concretely, computation in this step is performed by picking up or choosing the maximum value four wheel speeds of the respective wheels, as the estimated vehicle speed V B . Alternatively, in account of the condition where the vehicle is making a turn, the average value of left and right wheel speeds may be used as the estimated vehicle speed V B .
  • step G130 the wheel speed V W read at step G110 is subjected to a band-pass filtering process at sprung resonance frequencies of 1 to 2 Hz.
  • the thus filtered speed signal is amplified so that a sprung vibration estimation signal V US is computed.
  • the computed sprung vibration estimation signal V US is as shown in FIG. 18(b).
  • step G140 computes a wheel acceleration dV W by obtaining a rate of change per unit time of the wheel speed V W inputted at step G110.
  • step G150 the wheel acceleration dV W is subjected to a low-pass filtering process effected for frequencies around 20 Hz which is higher than frequencies of unsprung resonance components in the range of 10 to 15 Hz.
  • the filtered acceleration signal is amplified so that a filtered wheel acceleration dV a is computed.
  • the thus computed filtered wheel acceleration dV a is as shown in FIG. 18(c).
  • the filtered wheel acceleration dV a is subjected to a full-wave rectification process so that a filtered wheel acceleration absolute value dV b is computed.
  • the filtered wheel acceleration absolute value dV b is subjected to a filtering process using a filter having a predetermined time constant (for example, about 0.5 sec.) with the result that the filtered wheel acceleration absolute value dV b is smoothed and thus a road surface condition signal dV SP is computed.
  • the filtered wheel acceleration absolute value dV b and the road surface condition signal dV SP are as shown in FIGS. 18(d) and 18(e), respectively.
  • the wheel speed V W , estimated vehicle speed V B , sprung vibration estimation signal V US , wheel acceleration dV W , filtered wheel acceleration dV a , filtered wheel acceleration absolute value dV b and road surface condition signal dV SP are computed at steps G110-G160. Thereafter, the control procedure advances to step G170.
  • Step G170 compares the sprung vibration estimation signal V US with predetermined long-term vibration judgment levels (threshold levels) to discern the vehicle long-term vibration condition. Step G170 will be described below in greater detail with reference to FIG. 19.
  • a first threshold level L1 V US ⁇ L1
  • the long-term vibration judgment level X 07 is set to change from the level C to the level B when a predetermined delay period t2 expires after the sprung vibration estimation signal V US goes down below a return level (threshold level) L2'.
  • a change of the long-term vibration judgment level X 07 from the level B to the level A takes place upon expiration of a predetermined delay period t1 running after the sprung vibration estimation signal V US goes down below a return level (threshold level) L1'.
  • step G180 the road surface condition signal dV SP is compared with predetermined threshold levels for discerning the road surface condition (that is, the roughness of the road surface).
  • Step G180 will be described below in greater detail with reference to FIG. 20.
  • the road surface judgment level x 07 is set to switch from the level “c" to the level “b” when a predetermined delay period t4 elapses after the road surface condition signal dV SP goes down below a threshold level L4'.
  • the road surface judgment level x 07 changes from the level “b” to the level “a” upon an elapse of a predetermined delay period t3 after the road surface condition signal dV SP is less than a threshold level L3'.
  • step G190 sets an optimum damping force for the shock absorber based on the information obtained at steps G170 and G180.
  • the damping force of the shock absorber is set in a manner described below with reference to a map shown in FIG. 21.
  • the damping force is set to the hard state as in a conventional manner.
  • the damping force is set to the medium state.
  • the damping force is set to the hard state to thereby control or suppress the vibrations. Further, when the vehicle is running on the bad road, the damping force is set to the medium state.
  • step G190 After the damping force of the shock absorber is set at step G190, the control procedure returns to step G110.
  • the characteristic of the map shown in FIG. 21 is illustrative rather than restrictive, so that a map of a different character can be used.
  • the seventh embodiment described above may be modified in a manner described below.
  • Step G150 at which the wheel acceleration dV a is subjected to the low-pass filtering process having a transmittable frequency band of 20 Hz is replaced with a band-pass filtering process having a transmittable frequency band of 1-20 Hz.
  • these components having frequencies lower than 1 Hz are removed. It is, therefore, possible to remove or exclude fluctuating components caused by acceleration or deceleration.
  • the wheel acceleration dV a is prevented from increasing during accelerated or decelerated condition, so that the road surface condition judgment process at step G180 can be performed with an increased accuracy.
  • the frequency band of the above-mentioned band-pass filtering process is set in the range of 3-20 Hz. With this frequency band, it is possible to detect a road surface condition represented by these frequency components other than sprung resonance frequency and also prevent the wheel acceleration dV a from increasing during accelerated and decelerated conditions.
  • step G180 The procedure achieved at step G180 is replaced by a bad-road judgment procedure disclosed in Japanese Patent Laid-open Publication No. 60-596.
  • a suspension control system according to an eighth preferred embodiment of the present invention will be described below.
  • the eighth embodiment differs from the seventh embodiment in that the accelerated/decelerated condition of the vehicle is detected to alter the characteristic of a filter for precluding the possibility that the result of the long-term vibration judgment tends to indicates the occurrence of a long-term vibration due to an increase of the sprung vibration estimation signal VS during accelerated and decelerated conditions.
  • step H122 inputs a brake signal SW, a throttle opening signal, an engine speed (number of revolution) signal, a shift lever signal, a steering angle signal, etc.
  • a judgment is achieved to determine whether or not any one of the conditions (a)-(c) described above the reference to the sixth embodiment is satisfied.
  • a long-term vibration judgment correction flag X 08 is set to 1 ("ON" state).
  • the long-term vibration judgment correction flag X 08 may be set to the ON state when at least one or any combination of the conditions (a)-(c) is satisfied.
  • the accelerated/decelerated condition judgment (vehicle's longitudinal behavior judgment) executed at step H122 may be carried out in a manner described below.
  • a vehicle longitudinal acceleration which is obtained either directly from the wheel acceleration dV a or by filtering the wheel acceleration dV a , or a variation of the vehicle longitudinal acceleration is computed. Then, when the computed value exceeds a predetermined value, it is concluded that the vehicle is in an accelerated/decelerated condition and a longitudinal behavior of the vehicle occurs, and on the basis of this judgment, the long-term vibration judgment correction flag X 08 is set to the ON state.
  • the long-term vibration judgment correction flag X 08 is reset to 0 ("OFF" state).
  • step H122 When the conditions required for the long-term vibration judgment correction are not satisfied at step H122 and, hence, the vehicle is not in the accelerated or decelerated condition, this means that the long-term vibration judgment correction flag X 08 is in the OFF state. Then, the control procedure advances to step H131 at which a filtering process is achieved using a low-frequency side cutoff frequency which is lower than that used at step H134.
  • step H122 when the conditions required by step H122 are satisfied and hence the vehicle is in an accelerated/decelerated condition, this means that the long-term vibration judgment correction flag X 08 is set to the "ON" state.
  • the control procedure goes on to step H134 at which the characteristic of a band-bass filter used for computing the sprung vibration estimation signal V US is altered. More specifically, in order to reduce the effect of acceleration or deceleration, the low-frequency side cutoff frequency of the filter is increased (for example, from 0.5 Hz set at the time when the long-term vibration judgment correction flag X 08 is in the "OFF” state, to 1 Hz when X 08 is in the "ON” state).
  • a judgment as to whether or not any of the above-mentioned conditions (a)-(c) is satisfied is carried out to determine whether or not the long-term vibration correction flag is ON.
  • the characteristic of a filter used for calculation of the filtered wheel acceleration dV a is altered. More concretely, the filter characteristic is altered to perform only a low-pass filtering process with a cutoff frequency of 20 Hz.
  • a road surface condition signal dV SP calculated in the same procedure as step G160 shown in FIG. 17 increases during the accelerated or decelerated condition.
  • the road surface condition (roughness of a road surface) which is judged in the same procedure as step G180 is likely to be judged as a bad road during the accelerated or decelerated condition.
  • a damping force setting value which is calculated in the same procedure as step G190 is unlikely to represent the hard state during the accelerated or decelerated condition.
  • the tenth embodiment differs from the seventh embodiment in that the long-term vibration estimation signal is corrected in view of a signal representing an accelerated/decelerated condition of the vehicle. This correction will preclude the possibility that the long-term vibration judgment tends to represent the occurrence of a long-term vibration in view of an increase of the sprung vibration estimation signal during the accelerated or decelerated condition.
  • steps G170 through G190, in particular are replaced by the procedures shown in FIG. 23.
  • step J161 judges the vehicle's accelerated/decelerated condition (vehicle behavior estimation) in the same manner as done at step H122 of the eighth embodiment.
  • the long-term vibration judgment correction signal is set to 1 ("ON" state).
  • the long-term vibration judgment correction flag X 10 is reset to zero ("OFF" state).
  • Step 162 sets a correction coefficient K H for the sprung vibration estimation signal based on the ON-OFF state of the long-term vibration judgment correction flag X 10 .
  • the correction coefficient K H is set to a lower level.
  • the correction coefficient K H may be calculated from a map shown in FIG.
  • the map shown in FIG. 24 has a characteristic that dV a , dV B or ⁇ dV B on an axis of ordinates decreases with an increase of the correction coefficient K H on an axis of abscissas.
  • step J164 corrects the sprung vibration estimation signal VU S calculated at step G130 with the correction coefficient K H , thereby computing a corrected sprung vibration estimation signal V USH , as indicated by the following equation (3).
  • step J175 executes the same procedure as step G180 except that the corrected sprung vibration estimation signal V USH is compared with two predetermined return levels L1 and L2 for determining the nature of the long-term vibration.
  • the greater the road surface condition signal dV SP the smaller the corrected sprung vibration estimation signal V USH .
  • the greater the roughness of the road surface i.e., bad road
  • This embodiment is characterized by a control procedure in which long-term vibration judgment levels L1 and L2, return threshold levels L1' and L2', and delay periods t1 and t2 are switched according to the road surface condition (good road, average road, or bad road) judged based on the road surface condition signal dV SP .
  • step K180 executes the same procedure as step G180 so that the road surface condition is judged among three levels, that is, level "a” (good road), level “b” (average road) and level “c” (bad road), in accordance with the road surface condition signal dV SP . Thereafter, at steps K185, K195 and k205, long-term vibration judgment levels L1 and L2, return threshold levels L1' and L2', and delay periods t1 and t2 are set in correspondence to the road surface judgment level "a", "b” or "c” determined at step K180.
  • step K210 achieves the same procedure as step G170 with the exception that for the long-term vibration judgment levels L1 and L2, return threshold levels L1' and L2' and delay periods t1 and t2, those values set at step K185, K195 or K205 are used.
  • the long-term vibration judgment levels and the return threshold levels is so set as to gradually increase with a shift of the road surface judgment level in a direction from level "a" to level "b” and from level "b” to level "c”, so that a judgment result representing the occurrence of long-term vibration is more and more difficult to occur as the road surface condition becomes worse.
  • the judgment result representing the occurrence of a long-term vibration is difficult to come out.
  • the road surface judgment levels may be two or more levels set optionally, or a continuously varying level.
  • the long-term vibration judgment levels and return levels used in the eleventh embodiment described above are prepared as a function map of the vehicle speeds. More specifically, according to the twelfth embodiment, the long-term vibration judgment levels and return levels set at steps K185, K195 and K205 of the eleventh embodiment are determined by using a map in which these levels are variable with the vehicle speeds.
  • the map has a feature described below. In a vehicle speed range (40-60 km/h) in which the vehicle tends to cause long-term vibration, the long-term vibration judgment levels and the return levels are set to slightly higher levels.
  • the long-term vibration judgment levels and the return levels are set to slightly lower levels.
  • the long-term vibration of the vehicle is judged according to the vehicle speed so that an improved riding comfort can be obtained.
  • the long-term vibration judgment levels and the return levels are provided separately for each of the three different road surface conditions (good road, average road, and bad road).
  • the long-term vibration judgment levels and the return levels are provided separately for each of the three different road surface conditions (good road, average road, and bad road).
  • the delay periods t1 and t2 used in the eleventh embodiment described above are prepared as a function map of the vehicle speeds. More specifically, according to the thirteenth embodiment, the delay periods t1 and t2 which are set at steps K185, K195 and K205 of the eleventh embodiment are determined by using a map in which these delay periods are variable with the vehicle speeds.
  • the delay periods t1 and t2 may be prepared separately for each of the three different road surface conditions (good road, average road, and bad road), as shown in FIG. 26.
  • the delay periods t1 and t2 may be prepared separately for each of the three different road surface conditions (good road, average road, and bad road), as shown in FIG. 26.
  • This embodiment is characterized in that the characteristic of a filter is altered according to the road surface condition signal. More specifically, according to this embodiment, in accordance with the road surface condition (good road or bad road) which is judged based on the road surface condition signal dV SP , the characteristic of a filter used for extracting frequency components around the sprung frequencies is altered in such a manner that a long-term vibration judgment becomes more and more difficult with an increase in the roughness of the road surface. With the filter characteristic thus altered, the vehicle long-term vibration can be suppressed according to the road surface condition with the result that the riding comfort of the vehicle can be improved.
  • the road surface condition good road or bad road
  • the road surface condition is discerned among two levels (corresponding to the gad road and the good road, for example) based on the intensity of a road surface condition signal dV SP calculated in the same manner as step G160, and in accordance with the judged road surface condition level (good road or bad road), the characteristic of a band-pass filter used for calculating a sprung vibration estimation signal V US is altered.
  • a low-frequency side cutoff frequency of the band-pass filter is lowered (for example, from 3 Hz in a good-road running condition to 2 Hz in a bad-road running condition).
  • the degree of the band-pass filter is lowered (for example, from the primary filter in the good-road running condition to the secondary filter in the bad-road running condition).
  • an acceleration/deceleration detection means or sensor for detecting acceleration/deceleration of the vehicle.
  • a low-frequency side cutoff frequency and a high-frequency side cutoff frequency of a long-term vibration estimation filter, or the degree of the long-term vibration estimation filter is changed according to the accelerated/decelerated conditions (normal condition running at a constant speed, and an accelerated/decelerated condition) of the vehicle.
  • a long-term vibration suppressing control is achieved while taking into account of the accelerated/decelerated condition of the vehicle and changes of the road surface condition. As a result, the riding comfort of the vehicle is considerably improved.
  • the accelerated/decelerated condition and the road surface conditions may be judged in a manner other than as specified above. For example, multiple levels, a continuously varying level, or a mapping operation can be used for such judgment in order to perform a fine alteration of the cutoff frequency of the long-term vibration estimation filter or the degree of the long-term vibration estimation filter.
  • This embodiment is partly different from the seventh embodiment described above and is characterized in that a judgment on the long-term vibration is performed after the sprung vibration estimation signal V US is corrected based on the road surface condition signal dV SP .
  • a correction coefficient K H based on the road surface condition signal dV SP is calculated from maps shown in FIGS. 30 and 31.
  • step 0175 achieves the same procedure as step G170 excepting that the corrected sprung vibration estimation signal V USH is compared with predetermined long-term vibration judgment (return) levels L1 and L2 to discern the vehicle long-term vibration condition.
  • the corrected sprung vibration estimation signal V USH With an increase of the road surface condition signal dV SP , the corrected sprung vibration estimation signal V USH becomes small so that a result of judgment representing the occurrence of a long-term vibration is difficult to come out. Accordingly, a difficulty of setting the damping surface to the hard state increases with an increase in the roughness of the road surface.
  • the correction coefficient K H may be set for each of the switchable damping force levels. In this instance, it is also possible to realize the same control as done in the case where the long-term vibration judgement levels L1 and L2 and the return levels L1' and L2' are set separately for each of the different road surface conditions.
  • the sprung vibration estimated signal is corrected by a correction coefficient which may be provided in the form of a map prepared in conjunction with the vehicle speed. As shown in FIG. 32, a separate map is provided for each of three different road surface conditions (good road, average road and bad road).
  • the correction coefficient used for a speed range in which the vehicle tends to cause long-term vibration is set to a rather low level.
  • the correction coefficient is set to a rather high level.
  • delay periods t1 and t2 are variable with the road surface condition signal dV SP , as shown in FIG. 33. More specifically, the delay periods t1 and t2 decrease with an increase of the road surface condition signal dV SP . With the delay periods t1 and t2 thus set, the long-term vibration is suppressed and the bumpy feeling during a bad-road running can be eliminated.
  • FIG. 34 A description will now be given of a suspension control system according to an eighteenth preferred embodiment of the present invention.
  • This suspension control system is the same in construction as that in the seventh embodiment but the control operation thereof is partly different. That is, the threshold levels L1, L2, L1' and L2' are corrected based on the road surface condition signal dV SP , and thereafter the long-term vibration is judged.
  • the control operation of the eighteenth embodiment will be described in greater detail with reference to a flowchart shown in FIG. 34.
  • step P200 initializes the microcomputer. Thereafter, at step P210, the same procedures as steps G110-G160 are achieved so that a wheel speed V W , an estimated vehicle speed V B , a sprung vibration estimation signal V US , a wheel acceleration dV W , a filtered wheel acceleration dV a , a filtered wheel acceleration absolute value dV b , and a road surface condition signal dV SP are obtained.
  • two long-term vibration judgment basic levels 11 and 12 used for correcting the threshold levels L1 and L2 are calculated from a map shown in FIG. 35.
  • two long-term vibration return basic levels 11' and 12' used for correcting the threshold levels L1' and L2' are calculated from the map shown in FIG. 35.
  • the long-term vibration judgment basic levels 11 and 12 and the long-term vibration return basic levels 11' and 12' are variable with the estimated vehicle speed V a .
  • two correction coefficients K M and K H used for correcting the threshold levels L1, L2, L1' and L2' are calculated from a map shown in FIG. 36. As appears clear from FIG. 36, the correction coefficients K M and K H are variable with the road surface condition signal dV SP .
  • the threshold levels L1 and L2 are corrected in accordance with the following equations (4) and (5), using the long-term vibration judgment basic levels 11 and 12 and the correction coefficients K M and K H calculated respectively at step P220 and P240.
  • step P260 corrects the threshold levels L1' and L2' in accordance with the following equations (6) and (7), by using the long-term vibration return basic levels 11' and 12' and the correction coefficients K M and K H calculated respectively at step 230 and step 240.
  • the sprung vibration estimation signal V US is compared with the corrected threshold levels for discerning the long-term vibration. Step P270 will be described below in greater detail.
  • the long-term vibration judgment level X is changed from the level C to the level B when a predetermined period of time t2 expires after the sprung vibration estimation signal V US falls below the threshold level L2' (V US ⁇ L2' ).
  • the long-term vibration judgment level X is changed from the level B to the level A upon elapse of a predetermined period of time t1 following the condition of V US ⁇ L1'.
  • step P270 The judgment on the long-term vibration of the vehicle is thus completed at step P270.
  • the correction coefficients K M and K H are calculated from a road surface condition signal dV SP corresponding to sprung information and, by using these correction coefficients K M and K H , threshold levels L1 and L2 are corrected. Since the correction coefficients K M and K H increases with an increase of the road surface condition signal dVS p , as shown in FIG. 36, the threshold level L1 and L2 are corrected toward higher levels when the vehicle is running on the bad road.
  • This embodiment differs from the seventh embodiment in that there are provided a steering angle sensor for detecting a steering angle ⁇ , a throttle sensor for detecting a throttle opening judgment THR, and a stop-lamp sensor for judging whether or not a brake pedal is depressed, output signals from the respective sensors being inputted into the microcomputer.
  • the nineteenth embodiment is characterized in that information on vehicle attitude conditions obtained by a roll judgment, a dive judgment, a squat judgment or a high-speed running judgment are combined with unsprung information so as to set an optimum damping force, thereby softening the bumpy feeling caused by a roughness on the road surface and keeping an optimum vehicle attitude or position.
  • step Q300 initialization of the microcomputer 16 is performed at step Q300.
  • step Q301 a wheel speed V W , a steering angle ⁇ from the steering sensor, a stop lamp switch judgment STP from a stop lamp switch, and a throttle opening judgment THR from the throttle sensor are read or inputted in the microcomputer.
  • the steering angle ⁇ may be computed from the difference between a left wheel speed and a right wheel speed V WFR in a manner as indicated by the following equation (8). ##EQU2## where N is the steering gear ratio, L is the wheel base, W is the tread, K is the stability factor, V WFR is the wheel speed of right front wheel, and V WFL is the wheel speed of left front wheel.
  • the steering angle ⁇ is estimated and computed by a speed difference between the front wheels, however, it is possible to estimate the steering angle ⁇ through a calculation based on a speed difference between rear wheels.
  • step Q302 these procedures which are the same as those executed at steps G140-G160 and step G180 are executed whereby the wheel speed V W , a sprung vibration estimation signal V US , a wheel acceleration dV W , a filtered wheel acceleration dV a , a filtered wheel acceleration absolute value dV b and a road surface condition signal dV SP and obtained, and at the same time, a road surface judgment level "x" is obtained through a judgment on the roughness of the road surface (road surface condition).
  • step Q303 from the wheel speed V W is calculated an estimated vehicle speed V B based on which an acceleration dV b of the vehicle in a longitudinal direction (moving direction) of the vehicle is calculated. More concretely, the longitudinal vehicle acceleration dV B is calculated from a rate of change of the estimated vehicle speed V B , or from a rate of change of the wheel speed V W in a manner as disclosed in Japanese Patent Publication No. 1-47324.
  • the estimated vehicle speed V B is compared with predetermined threshold levels to discern a high-speed running among various attitude changes of the vehicle. Step Q304 will be described in detail with reference to FIG. 39.
  • a threshold level L5 V B ⁇ L5
  • V B >L6 it is concluded that the vehicle is running at a high speed
  • step Q305 a judgment is executed in accordance with the steering angle ⁇ and the estimated vehicle speed V B , so as to discern a roll of the vehicle among various vehicle attitude change conditions.
  • This step will be described in detail with reference to FIG. 40.
  • step Q306 the on-off state of the stop lamp switch judgment STP and the result of comparison made between the longitudinal acceleration dV B and predetermined threshold levels are used to discern a dive of the vehicle among various vehicle attitude change conditions. This step will be described below in detail with reference to FIG. 41.
  • step Q307 the on-off state of the throttle opening judgment THR and the result of comparison made between the longitudinal acceleration dV B and predetermined threshold levels are used to discern a squat of the vehicle among various vehicle attitude change conditions.
  • This step will be described below in detail with reference to FIG. 42.
  • step Q308 at which the attitude change judgment levels Y set at steps Q304-Q307, respectively, are compared with each other and the maximum level is set to a maximum value Y' of all the attitude change judgment levels.
  • the attitude change judgment levels have a relation G ⁇ H ⁇ I.
  • step Q309 an optimum damping force of the shock absorber is set based on the road surface judgment level "x" and the maximum value Y' among four attitude change judgment levels.
  • an optimum damping force setting operation is achieved with reference to a map shown in FIG. 43. As shown in FIG. 43, when the vehicle attitude change occurs while the vehicle is running on a good road or an average road, the damping force is set to the hard state.
  • the damping force is set to the medium state.
  • a bumpy feeling caused by a roughness on the road surface is substantially reduced and, at the same time, the vehicle is prevented from changing its attitude or posture and thus held in an optimum posture.
  • the damping force of the shock absorber is set to the hard state.
  • the characteristic of the map shown in FIG. 43 is illustrative rather than restrictive and, therefore, a map of a different character can be used.
  • suspension control system according to a twentieth preferred embodiment of the present invention.
  • the suspension control system of this embodiment is structurally the same as that of the nineteenth embodiment but the control operation thereof is partly different from that of the nineteenth embodiment.
  • the control operation of the twentieth embodiment will be described in greater detail with reference to a flowchart shown in FIG. 44.
  • step R400 performs initialization of the microcomputer. Then at step R401, the same procedures as G301-G303 shown in FIG. 17 are effected whereby the wheel speed V W , a steering angle ⁇ , a stop lamp switch judgment STP, a throttle opening judgment THR, a filtered estimated vehicle speed V US , a wheel acceleration dV W , a filtered wheel acceleration dV a , a filtered wheel acceleration absolute value dV b , a road surface condition signal dV SP , an estimated vehicle speed V B , and a longitudinal acceleration dV B are obtained.
  • step R420 computes, from a map shown in FIG. 45, roll judgment basic levels IRB and IRC used for correcting the threshold levels L7 and L8, and from a map shown in FIG. 46, dive judgment basic levels IDC and IDB used for correcting the threshold levels L9 and L10, and further from a map shown in FIG. 47, squat judgment basic levels ISC and ISD used for correcting the threshold levels L11 and L12.
  • IRB, IRC, IDC, IDB, ISC ISD are variable with the estimated vehicle speed V B .
  • step R430 from a map shown in FIG. 48 are calculated roll judgment correction coefficients KRB and KRC used for correcting the threshold levels L7 and L8. Similarly, dive judgment correction coefficients KDC and KDB used for correcting the threshold levels L9 and L10 are calculated from a map shown in FIG. 49. In addition, from a map shown in FIG. 50 are calculated squat judgment correction coefficients KSC and KSB used for correcting the threshold levels L11 and L12. As is apparent from FIGS. 48, 49 and 50, KRB, KRC, KDC, KDB, KSC and KSD are variable with the road surface conditions signal dV SP .
  • threshold levels L7-12 are corrected with the judgment basic level IRB, IRC, IDC, IDB, ISC and ISD computed at step R420 and the correction coefficients KRB, KRC, KDC, KDB, KSC and KSD computed at step R430, in accordance with the following equations (9)-(14).
  • correction coefficients KRB, KRC, KDC, KDB, KSC and KSD which are in turn used to correct the threshold levels L7-L12.
  • the correction coefficients KRB, KRC, KDC, KDB, KSC and KSD increase with an increase of the road surface condition signal dV SP , so that when the vehicle is running on a bad road, the threshold levels L7-L12 are so corrected as to become greater than before.
  • the suspension control system is provided with a mode selection switch which, upon actuation by an occupant (driver or passenger) of the vehicle, is able to switch the damping force of the shock absorber between two states, namely between a normal mode and a sport mode.
  • a mode selection switch which, upon actuation by an occupant (driver or passenger) of the vehicle, is able to switch the damping force of the shock absorber between two states, namely between a normal mode and a sport mode.
  • the damping force is set to a rather hard state.
  • the damping force is set to a rather soft state than the sport mode.
  • the shock absorber used in this embodiment likewise one used in any of the foregoing embodiments, has three switchable levels of damping force, namely low, medium and high levels (soft, medium and hard states).
  • the twenty-first embodiment is characterized by a control in which when a roughness on the road surface (a bump on the road surface or a sharp drop in road level) is detected in terms of a change of the front wheel speed in the state that the damping forces of the four shock absorbers are set to a level other than the low level (soft state), the damping force of a shock absorber provided for a rear wheel is temporarily altered to the low level (soft state).
  • a roughness on the road surface a bump on the road surface or a sharp drop in road level
  • the damping force of a shock absorber provided for a rear wheel is temporarily altered to the low level (soft state).
  • step S501 the microcomputer inputs the wheel sped V W .
  • step S502 the output from the mode selection switch is inputted at step S502 in preparation for determination of the current mode of the damping force of the shock absorbers.
  • step S503 the same procedures as steps G140-G160 are executed to compute a road surface condition signal dV SP .
  • step S504 executes the same procedures as step G120 to compute an estimated vehicle speed V B .
  • step S505 it is judged, from the output from the mode election switch inputted at step S502, whether the current setting of the mode selection switch corresponds to the normal mode or the sport mode. If the result at step S505 represents the sport mode, then the control advances to step S507. On the other hand, the result at step S505 indicates the normal mode, the control proceeds to step S506.
  • Step S506 judges whether or not the estimated vehicle speed V B is greater than a reference vehicle speed V B0 . If the result at step S505 is NO, it is concluded that the vehicle is running at a low speed, and the control advances to step S512 at which the damping force of the front wheel side and the damping force of the rear wheel side are both set to the soft state. On the other hand, if result at step S505 corresponds to the sport mode, or if the result at step S506 is YES, the control advances to step S507 at which the damping force of the front wheel side is set to the medium state.
  • Step S508 discerns the road surface condition to determine as to whether or not a bump is present on the road surface. As shown in FIG. 52(b), this step judges whether or not the road surface condition signal dV SPF related to the front wheels is in excess of a threshold level LA. If dV SPF >LA, a counter TA associated with the microcomputer stars counting. The counting operation of the counter TA continues until a predetermined time period tA expires after the front wheel side road surface condition signal dV SPF falls below the threshold level LA.
  • step S508 If dV SPF ⁇ LA at step S508, it is concluded that there is no bump on the road surface, and the control advances to S513 at which the damping force of the rear wheel side is set to the medium state. On the other hand, if dV SPF >LA, it is judged that a bump is present on the road surface, and control advances to step S509 which in turn judges whether or not a wheel base delay TD has passed after the front wheel side road surface condition signal dV SPF exceeded the threshold level LA.
  • the wheel base delay TD is calculated, for example, from the following equation (15).
  • step S509 When the result at step S509 indicates that the wheel base delay TD has not expired from the time when the front wheel side road surface condition signal dV SPF became greater than the threshold level LA, it is concluded that the bump on the road surface has cleared the front wheels and is now located between the front wheels and the rear wheels, and the control goes on to step S513 at which the damping force of the rear wheel side is set to the medium state.
  • step S513 On the other hand, if the wheel base delay TD has elapsed since dV SPF >LA, it is judged that the rear wheels have just cleared the bump or the rear wheels are now clearing the bump, then the control advances to step S510.
  • Step S510 judges whether or not a soft hold time TB has expired from the time when the rear wheel side damping force was set to the soft state.
  • the soft hold time TB is equal to the count number of the counter TA and, hence, it may be said that step S510 judges whether or not a certain time period has elapsed, which time period is equal in length to the time period spent by the front wheels for clearing the bump on the road surface.
  • step S510 indicates an elapse of the soft hold time TB, it is judged that the rear wheels have passed the bump, and the control advances to step S513 at which the rear wheel side damping force is set to the medium state.
  • the result at step S510 indicates that the soft hold time TB still continues, then the control goes on to step S511 at which the rear wheel side damping force to the soft state.
  • the damping force of the rear wheel side is set to the soft state for a soft hold time TB which is equal in length to the time period needed for the front wheels to clear the bump.
  • the wheel base delay TD is provided.
  • the rear wheel side damping force may be switched to the soft side immediately after a bump on the road surface is detected by the front wheels.
  • the suspension control system is provided with a brake judgment switch for judging whether or not a brake pedal is depressed, a throttle judgment switch for judging whether or not a throttle pedal is depressed, and an engine rotation sensor for detecting a change of the engine speed.
  • the outputs from these switch and sensor are inputted to the microcomputer.
  • This embodiment is characterized in that the damping force of the shock absorber is altered in view of sprung resonance frequency components contained in a wheel speed signal and longitudinal speed components generated due to acceleration and deceleration of the vehicle.
  • the damping force of each shock absorber is switchable between two states, namely between the soft state and the hard state.
  • step T601. the microcomputer is initialized at step T601.
  • step T602 a wheel speed V W related to each wheel is inputted.
  • step T603 computes an estimated vehicle speed V B and a sprung vibration estimation signal V US in the same manner as done at steps G120 and G130 shown in FIG. 17.
  • step T604 a brake signal and a throttle signal are inputted for discerning a longitudinal behavior of the vehicle.
  • a longitudinal behavior judgement signal Z is turned on and thereafter holds its ON state for a predetermined period of time TE, as shown in FIG. 54.
  • a judgement level K a and a return level (end level) K b are determined by using a map stored in the microcomputer. This map is as shown in FIG. 55.
  • the judgement level K a and the return level K b vary with the estimated vehicle speed V B . More specifically, they are set to have higher levels as the vehicle speed increases. In other words, in view of the fact that the entire vehicle behavior becomes greater with an increases of the vehicle speed, the damping force is set to hard to switch to the hard state.
  • the map shown in FIG. 55 should be construed as illustrative rather than restrictive, and a map of a different character can be used.
  • Step T606 judges whether or not the damping force of the shock absorber is set to the hard state.
  • the control goes on to step T607.
  • Step T607 judges whether or not the sprung vibration estimation signal V US is greater than or equal to the judgement level K a . If the result at step T607 is NO, it is concluded that vibration components having frequencies around the sprung resonance frequency are small and hence no long-term vibration of the vehicle is generated, and the control advances to step T608 at which the damping force of the shock absorber is set to the soft state.
  • step T607 if the result at step T607 is YES, it is concluded that vibration components having frequencies around the sprung resonance frequency are great and hence a long-term vibration is generated, and the control goes on to step T612 at which the damping force of the shock absorber is set to the hard state.
  • Step T609 judges, from the longitudinal behavior judgement signal Z and the sprung vibration estimation signal V US , whether or not a longitudinal vehicle behavior is actually generated.
  • the sprung vibration estimation signal V US is greater than or equal to the judgement level K a and when the longitudinal behavior judgement signal Z is "off"
  • the vehicle is running on a wavy road and a vehicle long-term vibration is generated.
  • Step T613 judges whether or not the damping force is to be set to the soft state or to the hard state in view of the degree of acceleration/deceleration.
  • the control advances to step T608 at which the damping force of the shock absorber is set to the soft side.
  • step T614 the control goes on to step T614 at which the damping force of the shock absorber is set to the hard state for a predetermined period of time.
  • step T608 the damping force of the shock absorber is set to the hard state.
  • step T609 When the result at step T609 indicates the occurence of a long-term vibration, then the control advances to step T610 at which the sprung vibration estimation signal V US is compared with the return level K b . In this instance, if V US ⁇ K b , the control goes on to step T612 at which the damping force of the shock absorber is set to the hard state, thereby preventing the generation of a long-term vibration. On the other hand, if V US ⁇ K b , the control advances to step T611. Step T611 judges whether or not a delay period T0 from the instance where the sprung vibration estimation signal V US becomes below the return level K b has expired.
  • step T608 the delay period TD has already expired, it is concluded that the vehicle long-term vibration has been suppressed, and the control advances to step T608 at which the damping force of the shock absorber is set to the soft state.
  • step T608 the delay period TD has not expired, it is concluded that the vehicle long-term vibration is still existing.
  • the control goes on to step T612 at which the damping force of the shock absorber is set to the hard state and thus prevents the generation of a long-term vibration.
  • a vehicle long-term vibration condition representing sprung information is combined with a longitudinal vehicle behavior condition so as to preclude the unnecessary setting of the damping force to the hard state which would otherwise occur when the vehicle is running on a good road.
  • a satisfactory riding comfort is maintained. Only when the vehicle is running on a wavy road, the damping force of the shock absorber is set to the hard state to prevent generation of a long-term vibration, thereby improving the riding comfort of the vehicle.
  • the condition of a longitudinal vehicle behavior is determined based on a brake signal and a throttle signal. If a fine control is necessary, a steering signal, an engine speed signal, and a shift-lever signal may be used in combination with the brake signal and the throttle signal.
  • steps T606-T614 of the twenty-second embodiment shown in FIG. 53 can be replaced with steps T620-T634 of a twenty-third embodiment shown in FIG. 56.
  • Step T620 is effected to avoid an erroneous long-term vibration judgment which may be caused when a longitudinal vehicle behavior is estimated. To this end, step T620 judges whether or not any of the conditions (a)-(c) described above with respect to the sixth embodiment is satisfied.
  • a long-term vibration judgment inhibition flag X 06 is set to 1 (ON state), as shown in FIG. 57.
  • An engine acceleration is computed after an engine pulse signal is inputted at step T604 shown in FIG. 53.
  • the long-term vibration judgment inhibition flag X 06 at least one or any combination of the conditions (a)-(c) can be used.
  • step T622 When the required condition for inhibiting the long-term vibration judgment is not satisfied, that is, when the long-term vibration judgment inhibition flag X 06 is reset to zero (OFF state), the control advances to step T622 at which a judgment is carried out to determine as to whether a long-term vibration is generated and the damping force is set to the hard state.
  • step T622 If the result at step T622 indicates the setting of the damping force to the soft state, the control advances to step T624 at which a judgment is achieved to determine as to whether the sprung vibration estimation signal V US is greater than or equal to the judgment level K a .
  • the control goes on to stop T632 at which the damping force of the shock absorber is set to the soft state.
  • step T624 if the result at step T624 is YES, it is concluded that vibration components having frequencies around the sprung resonance frequency are great and hence a long-term vibration is generated. Then, the control advances to step T634 at which the damping force of the shock absorber is set to the hard state.
  • step T622 When the result at step T622 indicates that the damping force is set to the hard state, then the control goes on to step T628.
  • step T628 the sprung vibration estimation signal V US is compared with the return level K b . In this instance, if V US ⁇ K b , then the control goes on to step T634 at which the damping force of the shock absorber is set to the hard state, thereby preventing generation of a long-term vibration.
  • step T630 On the other hand, if V US ⁇ K b , then the control advances to step T630 at which a judgment is achieved to determine whether or not a delay time TD from the instance of V US ⁇ K b has expired.
  • step T362 the delay time TD has already expired, it is concluded that the vehicle longterm vibration has been suppressed, and the control goes on to step T362 at which the damping force of the shock absorber is set to the soft state.
  • step T634 the delay time TD has not expired, it is concluded that the long-term vibration is still existing, and the control advances to step T634 at which the damping force of the shock absorber is set to the hard state, thereby suppressing the vehicle long-term vibration.
  • the long-term vibration judgment inhibition flat X 06 is ON at step T620, this means that the vehicle is in accelerated or decelerated condition and a longitudinal vehicle behavior is generated. In this condition, the sprung vibration estimation signal V US becomes great and, hence, the standing condition may be erroneously judged as involving the generation of a long-term vibration.
  • a judgment is executed at step T626 so as to determine whether or not the damping force has already been set to the hard state owing to a long-term vibration occurred at the preceding cycle of control operation. If the result at step T626 is NO, this means that the damping force is set to the soft state.
  • step T632 the control advances to step T632 and thus maintains the damping force in the soft state.
  • step T626 if the result at step T626 is YES, this means that the damping force has already been set to the hard state due to the presence of the prior stay.
  • step T630 a judgment is made to determine whether or not the delay time TD from the instance of V US ⁇ K b has expired. When the delay time TD has expired, it is concluded that the long-term vibration has been suppressed, and the control advances to step T632 at which the damping force of the shock absorber is set to the soft state.
  • step T634 the damping force of the shock absorber is set to the hard state, thereby preventing the generation of a long-term vibration.
  • step T632 or step T634 When the procedure at step T632 or step T634 has completed, the control operation is terminated.
  • the condition of a long-term vibration representing sprung information is combined with a longitudinal vehicle behavior condition as shown in FIG. 57, so as to preclude the unnecessary setting of the damping force to the hard state which would otherwise occur when the vehicle is running on a good road.
  • a satisfactory riding comfort is maintained. Only when the vehicle is running on a wavy road, the damping force of the shock absorber is set to the hard state to prevent generation of a long-term vibration, thereby improving the riding comfort of the vehicle.
  • a condition (d) which requires that the engine speed is smaller than a predetermined speed (for example, 300 rpm).
  • This condition (d) will supplement the condition (c) when an engine speed signal is not available due to a break in the wire.
  • step T620 FIG. 56
  • the control advances to step T632 for returning the damping force of the shock absorber to the i condition (soft state) before the control is effected.
  • an appropriate process for holding the damping force in a fixed level may be performed.
  • the long-term vibration judgment inhibition flag As a condition for setting the long-term vibration judgment inhibition flag, it is possible to use a signal representing an accelerated or decelerated condition, such as a wheel acceleration dV W signal or a variation of the wheel acceleration dV W . In this instance, if the result at step T620 indicates the presence of an accelerated or decelerated condition, the long-term vibration judgment inhibition flag is set to ON and, subsequently, the same procedures as done in the twenty-third embodiment are executed.
  • an accelerated or decelerated condition such as a wheel acceleration dV W signal or a variation of the wheel acceleration dV W .
  • This embodiment is characterized in that a vehicle behavior is detected by using sprung information on a wheel speed difference.
  • step U702 a right wheel speed V WR and a left wheel speed V WL are inputted to the microcomputer.
  • step U704 computes a speed difference V RL between the right wheel speed V WR and the left wheel speed V WL that are inputted at step U702.
  • the speed difference V RL thus computed is then subjected to a band-pass filtering process using a band-pass filter (B.P.F.) passing only those components having frequencies (1-3 Hz) around the sprung resonance frequency.
  • B.P.F. band-pass filter
  • a judgment level K c for discerning the occurrence of a roll of the vehicle and a return level (end level) K d are determined by using a map stored in the microcomputer. This map is as shown in FIG. 59.
  • the judgment level K c and the return level K d vary with the vehicle speed. More specifically, they are set to have higher levels as the vehicle speed increases. In other words, as the vehicle speed becomes great, it becomes more and more difficult to switch the damping force to the soft state for a purpose of maintaining a sufficient stability during a high-speed running.
  • the map shown in FIG. 59 should be construed as illustrative rather than restrictive, and a map of a different character can be used.
  • Step U706 judges whether or not the damping force of the shock absorber is set to the hard state.
  • the control goes on to step U707.
  • Step U707 judges whether or not the filtered speed difference V RL * is greater than or equal to the judgment level K c . If the result at step U707 is NO, it is concluded that vibration components having frequencies around the sprung resonance frequency are small and hence no rolling is generated, and the control advances to step U708 at which the damping force of the shock absorber is set to the soft state. On the other hand, if the result at step U707 is YES, the control goes on to step U711 at which the damping force of the shock absorber is set to the hard state.
  • step U706 When the result at step U706 represents the damping force of the shock absorber set to the hard state, then the control goes on to step U709 at which the filtered speed difference V RL * is compared with the return level K d . In this instance, if V RL * ⁇ K d , then the control goes on to step U711 at which the damping force of the shock absorber is set to the hard state, thereby preventing the vehicle from rolling. On the other hand, if V RL * ⁇ K d , the control advances to step U710 at which a judgment is made to determine whether or not the delay time TE from the instance of V US ⁇ K b has expired.
  • step U708 the damping force of the shock absorber is set to the soft state.
  • step U711 the damping force of the shock absorber is set to the hard state, thereby preventing the generation of a rolling.
  • step U708 or step U711 When the procedure at step U708 or step U711 has completed, the control operation is terminated.
  • a vehicle roll condition is determined based on the speed difference between right and left wheel speeds, as shown in FIG. 60.
  • a difference in speed between the left and right wheels is used for judging the vehicle roll condition. So far as the judgment of the vehicle behavior depending on the speed difference is concerned, various modifications are possible. For example, the occurrence of a pitching or a bouncing of the vehicle may be judged on the basis of a difference in speed of front and rear wheels. Similarly, a difference in speed of two diagonally opposed wheels may be used to determine the occurrence of a rolling ("warp") about an axis interconnecting the diagonally opposed wheels.
  • a right wheel speed V WR a left wheel speed V WL , and a steering angle ⁇ calculated in accordance with equation (1) or (8) specified above are inputted at steps V802, V803 and V804, respectively.
  • the steering angle ⁇ may be inputted via a steering angle sensor provided separately.
  • a vehicle speed V B is computed according to the following equation (16).
  • the actual yaw rate Y is differentiated with time to compute a yaw acceleration dY.
  • a return level K e used for judging yawing is determined by using a map stored in the microcomputer.
  • step V808 judges whether or not the damping force of the shock asorber is set to the hard state. If the result at step V808 is NO, that is, when the damping force is set to the soft state, then the control advances to step V809 at which a judgment on the turning condition is executed using a map shown in FIG. 62. In order to judge the vehicle turning condition, a value which is determined by the vehicle speed V B and the steering angle ⁇ is compared with a threshold level ⁇ , as shown in FIG. 62.
  • step V809 When the result at step V809 is NO, that is, when the value determined by V B and ⁇ is smaller than the threshold level ⁇ , it is concluded that the vehicle is making a gentle turn or running without turn, and the control goes on to step V810 at which the damping force of the shock absorber is set to the soft state. On the other hand, when the result at step V809 is YES, then the control goes on to step V813. Thus, the damping force of the shock absorber is set to the hard state at step V813 so that it is possible to dampen a rolling motion caused when the vehicle is making a turn.
  • step V808 represents the hard state setting of the damping force
  • the control goes on to step V811 at which the aw acceleration dY is compared with the return level K e .
  • step V813 at which the damping force of the shock absorber is set to the hard state, thereby dampening the vehicle roll.
  • step V812 the control advances to step V812 at which a judgment is executed to determine whether or not a delay time TF from the instance when dY ⁇ K e has expired.
  • step V810 the damping force of the shock absorber is set to the soft state.
  • step V813 the damping force of the shock absorber to the hard state so that the roll will not occur.
  • step V810 or step V813 When the procedure at step V810 or step V813 has completed, the control operation is terminated.
  • the damping force of the shock absorber is set to the hard state. Thereafter, the yaw acceleration dY estimated by the right and left wheel speeds becomes equal to the predetermined level K e , and when the delay time has expired since then, the damping force of the shock absorber is set to the soft state. It is, therefore, possible to control the roll caused by a steering operation so that the riding comfort is improved.
  • the output signals from the respective wheel speed sensors are processed in the microcomputer 16 to obtain variations of the wheel speeds, and based on the wheel speed variations, the road surface condition is detected to control the suspension.
  • the road surface condition is detected by the degree of periodic fluctuation of the output signals (output voltages) of the wheel speed sensors.
  • a bracket used for attaching the wheel speed sensor to the knuckle portion of a suspension resonates with the unsprung vibration so that the output voltage of the sensor is fluctuated.
  • a suspension control system generally comprises four wheel speed sensors 11, 12, 13 and 14, a periodically fluctuating component extracting means or unit 26A for extracting periodically fluctuating amplitude components V We26 from the output signal V W26 , a resonance frequency band-pass filter 26B for extracting sprung resonance frequency components V Wu26 and unsprung resonance frequency components V W126 from the periodically fluctuating components V We26 , an analog-to-digital (A/D) converter 26C for digitizing the sprung resonance frequency components V Wu26 and unsprung resonance frequency components V W126 , and a microcomputer 26D for inputting the output signal from the A/D converter 26C and detecting the road surface condition.
  • A/D analog-to-digital
  • the periodically fluctuating component extracting unit 26A includes an amplifier 26a for amplifying the output voltage signal V W26 , a full-wave rectifier 26b for extracting absolute value components of the signal amplified by the amplifier 26a, and a smoothing filter 26c for smoothing the absolute value components extracted by the full-wave rectifier 26b and thus extracting the periodically fluctuating components V We26 .
  • FIG. 65 shows waveforms of a wheel speed signal outputted from a wheel speed sensor when a vehicle is running on a road having different grades of road surface conditions, a periodically fluctuating component V We26 signal, a sprung resonance frequency component V Wu26 signal, and an unsprung resonance frequency component V W126 signal.
  • V We26 a periodically fluctuating component
  • V Wu26 a sprung resonance frequency component
  • V W126 an unsprung resonance frequency component
  • FIG. 67 is a flowchart illustrating a control procedure or routine executed in the microcomputer 26D.
  • the microcomputer 26D executes initialization at step W100.
  • digital signals converted by the A/D converter 26C are inputted at step W105.
  • step W125 a digitized sprung resonance frequency component V Wu26 signal and a digitized unsprung resonance frequency component V W126 signal are compared with a judgment level, so that it is possible to discriminate different grades of road surface conditions (good or flat road, wavy road, busy road and complex road).
  • FIG. 68 differs from the foregoing twenty-sixth embodiment in that the periodically fluctuating component V Wd26 signal is converted by an A/D converter 26C into a digital signal which in turn is inputted into the microcomputer 26d. Then, sprung resonance frequency component V Wu26 signal and unsprung and resonance frequency component V W126 signal are extracted through a data processing operation executed under the control of software used in the microcomputer 26D.
  • FIG. 69 is a flowchart showing the control operation executed in the microcomputer 26D. At step X100, the microcomputer executes initialization.
  • step X105 a digital signal V Wd26 converted by the A/D converter 26C is inputted to the microcomputer 26D.
  • step X115 the digital signal V Wd26 is subjected to a band-pass filtering process using a band-pass filter which passes only those components having frequencies around the sprung resonance frequency and the unsprung resonance frequency, so that a sprung resonance frequency component V Wu26 signal and an unsprung resonance frequency component V W126 signal are computed.
  • step X125 executes the same procedure as the step W125, so that the road surface condition is determined.
  • an appropriate mapping operation may be employed to estimate the road surface conditions in terms of a continuously varying level.
  • the unsprung resonance frequency component V W126 may be converted into a signal of the nature obtained after a full-wave rectification and smoothing, and on the basis of the thus converted signal, a judgment on the road surface condition is achieved.
  • fz is the output fluctuating frequency caused by the eccentricity
  • r is the radius of tires
  • V is the vehicle speed
  • the wheel speed sensor may be of the type having an electromagnetic pickup coil or a Hall element, or alternatively of the type which detects a change in the magnetic resistance. Irrespective of the type of detection element used, a satisfactory wheel speed sensor is of the electromagnetic type having an air gap and constructed to output a signal corresponding to an angular velocity or an angle of rotation of the wheel.
  • the road surface condition may be judged on the basis of the sprung resonance frequency component V Wu26 or the unsprung resonance frequency component V W126 .
  • the shock absorber having plural modes defining the switchable levels of damping force may be of the construction in which the damping force is switchable either stepwise or linearly.
  • the spring constant of a spring and/or the stiffness of a stabilizer may be changed simultaneously with the switching of the damping force of the shock absorber.
  • the signals which are used as representing sprung information and unsprung information may be a wheel speed signal or a wheel acceleration signal.
  • the amount of variance or fluctuation of the wheel speed increases with an increase in the vehicle speed. Since the sprung vibration estimation signal V US is obtained by filtering fluctuating components of the wheel speed, the thus obtained sprung vibration estimation signal V US , as against the actual sprung vibration, has a tendency to increase with the vehicle speed. In order to rectify the tendency, the long-term vibration judgment level is increased with an increase in the vehicle speed.
  • the sprung vibration estimation signal V US may be corrected with a correction coefficient which is set to decrease with an increase in the vehicle speed.
  • the sprung vibration estimated signal VU S when corrected with the correction coefficient is no longer possible to exceed the actual sprung vibration when the vehicle is running at a high speed.
  • the drive wheels In general, so far as the drive wheels are concerned, fluctuating components of the torque of an engine or a transmission system are superimposed on fluctuating components of the wheel speed.
  • the drive wheel might slip on such a road surface which has a low friction coefficient or can provide only a low road holding characteristic between itself and tires.
  • the wheel speed which is used for estimating the sprung vibration is represented by the wheel speed of a wheel other than drive wheels or a wheel supplying a smaller driving power.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Vehicle Body Suspensions (AREA)
  • Fluid-Damping Devices (AREA)
US07/896,930 1991-06-10 1992-06-10 Suspension control system for controlling suspension of automotive vehicle based on wheel speed data Expired - Fee Related US5444621A (en)

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Application Number Priority Date Filing Date Title
JP13800991 1991-06-10
JP3-138009 1991-11-11
JP3-294658 1991-11-11
JP29465891 1991-11-11
JP4063916A JP2917652B2 (ja) 1991-06-10 1992-03-19 サスペンション制御装置
JP4-063916 1992-03-19

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